During a drilling operation, data may be transmitted from a downhole transmitter located on a downhole tool included as part of the bottom hole assembly (BHA) of a drill string positioned in a wellbore. Data transmitted from the downhole transmitter may include, for instance, properties of the surrounding formation, downhole conditions, status of downhole equipment, orientation of the downhole equipment, and the properties of downhole fluids. Electronics present in the BHA may be used for transmission of data to the surface, collecting data using sensors such as vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, and acoustic detectors, acquiring images, measuring fluid flow, determining direction, emitting signals, particles or fields for detection by other devices, interfacing with other downhole equipment, and sampling downhole fluids. The BHA may also include mud motors and steerable drilling systems, such as a rotary steerable system (RSS), which may be used to steer the wellbore as the wellbore is drilled. By receiving data from the BHA, an operator may have access to the data collected by the sensors.
The drill string can extend thousands of feet below the surface. Typically, the bottom end of the drill string includes a drill bit for drilling the wellbore. Drilling fluid, such as drilling mud, may be pumped through the drill string. The drilling fluid typically cools and lubricates the drill bit and may carry cuttings back to the surface. Drilling fluid may also be used for control of bottom hole pressure. In situations where the formation may be damaged by the pressure generated by the column of drilling fluid, mist or foam may be used to reduce the pressure on the formation due to the fluid column.
Examples of telemetry systems for transmitting data to the surface include mud pulse (MP), electromagnetic (EM), hardwired drill pipe, fiber optic cable, and drill collar acoustic systems. Traditionally, MP and EM telemetry may be less expensive to deploy than hardwired drill pipe, fiber optic cable and drill collar acoustic systems. An EM system may operate when pumps are not operating to circulate fluid through the drill string, which, in certain operations, may be necessary for use of MP systems. In certain traditional uses, an EM telemetry system may transmit data at a higher data rate compared to an MP system. EM systems may also operate when foam or mist are used as a drilling fluid which may hinder the generation or reception of mud pulses of sufficient amplitude for reliable MP telemetry. EM systems may be limited in depth of reliable operation due to attenuation of the signal received at surface, i.e., EM signals, may be reduced to an amplitude that is below the noise level generated by various pieces of drilling equipment used to drill the well.